Pairing-specific, activity-dependent presynaptic facilitation at Aplysia sensory-motor neuron synapses in isolated cell culture

Long-term plasticity can differ from short-term in recruiting the growth of new synaptic connections, a process that requires the participation of both the presynaptic and postsynaptic components of the synapse. How does information about synaptic plasticity spread from its site of origin to recruit the other component? The answer to this question is not known in most systems. We have investigated the possible role of spontaneous transmitter release as such a transsynaptic signal. Until recently, relatively little has been known about the functions of spontaneous release. In this paper, we report that spontaneous release is critical for the induction of a learning-related form of synaptic plasticity, long-term facilitation in Aplysia. In addition, we have found that this signaling is engaged quite early, during an intermediate-term stage that is the first stage to involve postsynaptic as well as presynaptic molecular mechanisms. In a companion paper, we show that spontaneous release from the presynaptic neuron acts as an orthograde signal to recruit the postsynaptic mechanisms of intermediate-term facilitation and initiates a cascade that can culminate in synaptic growth with additional stimulation during long-term facilitation. Spontaneous release could make a similar contribution to learning-related synaptic plasticity in mammals.serotonin | cell culture | miniature excitatory postsynaptic current | octopamine | botulinum toxin S pontaneous transmitter release was discovered 60 y ago by Fatt and Katz (1), who found that it represents the quantal unit of transmitter release evoked by a presynaptic action potential. However, until recently, relatively little has been known about other possible functions of spontaneous release. In the last few years, we have learned that spontaneous release can contribute to postsynaptic firing (2, 3), regulation of postsynaptic kinase pathways (4), and maintenance of postsynaptic dendritic spines and receptors (5, 6). Spontaneous release has also been found to contribute to some cases of homeostatic scaling of synaptic strength (7-14). Here we report a role of spontaneous transmitter release in the induction of a learning-related form of synaptic plasticity, longterm facilitation produced by serotonin (5HT) in Aplysia.Long-term plasticity can differ from short-term in recruiting the growth of new synaptic connections, a process that requires the participation of both the presynaptic and postsynaptic components of the synapse (15-21). Because short-term plasticity often involves only one component of the synapse (22-24), the question arises: How does information about synaptic plasticity spread from its site of origin to recruit the other component of the synapse? Studies of synaptic growth during development have revealed a fairly elaborate program of pre-and postsynaptic changes involving a variety of orthograde and retrograde messengers (25), including activity-dependent or spontaneous release of the transmitter itself (26-30). We have now investigated the possible role of spo...

Section: Methodsmentioning

confidence: 99%

Spontaneous transmitter release is critical for the induction of long-term and intermediate-term facilitation inAplysia

Jin

Puthanveettil

Udo

et al. 2012

“…Intracellular recordings were made from a single siphon sensory (LE) neuron (21) and a single small siphon (LFS) motor neuron (19). The neurons were impaled with micropipettes (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) Mfl) filled with a solution of 2.0 M potassium acetate, 0.5 M potassium chloride, and 10 mM Hepes (pH 7.2). Recordings were made using an Axoclamp 2A amplifier (Axon Instruments, Foster City, CA) and the data were stored on a modified VHS recorder (Model 400, A. R. Vetter, Rebersburg, PA).…”

Section: Methodsmentioning

confidence: 99%

Enhancement of sensorimotor connections by conditioning-related stimulation in Aplysia depends upon postsynaptic Ca2+.

Murphy

Glanzman

1996

Classical conditioning of Aplysia's siphonwithdrawal reflex is thought to be due to a presynaptic mechanism-activity-dependent presynaptic facilitation of sensorimotor connections. Recent experiments with sensorimotor synapses in dissociated cell culture, however, provide an alternative cellular mechanism for classical conditioningHebbian long-term potentiation (LTP) of sensorimotor connections. Induction of Hebbian LTP of these connections is mediated by activation ofN-methyl-D-aspartate-related receptors and requires the postsynaptic elevation of intracellular Ca2+. To determine whether the enhancement of sensorimotor synapses during classical conditioning inAplysia-like LTP of sensorimotor synapses in culture-also depends upon the elevation of postsynaptic Ca2 , we carried out experiments involving the cellular analog of classical conditioning of siphon withdrawal. We examined changes in the strength of monosynaptic siphon sensorimotor connections in the abdominal ganglion of Aplysia following paired presentations of sensory neuron activation and tail nerve shock This training regimen resulted in significant enhancement of the monosynaptic sensorimotor excitatory postsynaptic potential, as compared with the sensorimotor excitatory postsynaptic potential in preparations that received only test stimulation. Infusing the motor neuron with 1,2-bis(2-aminophenoxy)ethane-N,N-N',N'-tetraacetic acid, a specific chelator of intracellular Ca2+, prior to paired stimulation training blocked this synaptic enhancement. Our results implicate a postsynaptic, possibly Hebbian, mechanism in classical conditioning in Aplysia.Classical conditioning of the siphon-withdrawal reflex in the marine molluskAplysia (1, 2) is thought to be mediated, in part, by changes in the strength of the monosynaptic connections between sensory and motor neurons in the abdominal ganglion. According to a prominent model (3, 4), the pairing of action potentials in sensory neurons induced by the conditioned stimulus (CS)-weak tactile stimulation of the animal's siphon or mantle-with activation of facilitatory interneurons induced by the unconditioned stimulus (US)-electrical shocks delivered to the animal's tail-leads to increased neurotransmitter release by the sensory neurons with subsequent siphon stimulation. This enhancement of sensorimotor synaptic transmission is associative because greater enhancement is produced by paired CS-US stimulation than by unpaired (CS-) stimulation, or by presentation of the US alone (3, 4). The cellular mechanism that underlies this associative synaptic change-known as "activity-dependent (enhancement of) presynaptic facilitation" (3) or "activity-dependent neuromodulation" (4)-is thought to be due exclusively to presynaptic processes (3-6).Recent experiments (7,8) (19). Thus, paired CS-US stimulation during classical conditioning training would be expected to result in a pattern of neuronal activity within the central nervous system of Aplysia similar to that used to induce LTP of sensorimotor synapses in ce...

“…4 A and B) in which the reflex is mediated in part by monosynaptic excitatory postsynaptic potentials (EPSPs) from LE siphon sensory neurons to LFS siphon motor neurons in the abdominal ganglion (30). Sensitization is due in part to presynaptic facilitation of those EPSPs by PKA (43,44) and conditioning to activity-dependent facilitation of the EPSPs (28), which involves two mechanisms that interact (29): activity-dependent enhancement of the facilitation due to Ca 2+ priming of adenylyl cyclase and greater production of cAMP and activation of PKA in the sensory neurons (43)(44)(45)(46)(47)(48)(49)(50)(51), and Hebbian potentiation due to Ca 2+ influx through NMDA-like receptor channels in the motor neurons (52)(53)(54)(55).…”

Section: Hcn Channels Contribute To Behavioral Conditioning But Notmentioning

confidence: 99%

Hyperpolarization-activated, cyclic nucleotide-gated cation channels in Aplysia : Contribution to classical conditioning

Yang

Kuzyk

Antonov

et al. 2015

Hyperpolarization-activated, cyclic nucleotide-gated cation (HCN) channels are critical regulators of neuronal excitability, but less is known about their possible roles in synaptic plasticity and memory circuits. Here, we characterized the HCN gene organization, channel properties, distribution, and involvement in associative and nonassociative forms of learning in Aplysia californica. Aplysia has only one HCN gene, which codes for a channel that has many similarities to the mammalian HCN channel. The cloned acHCN gene was expressed in Xenopus oocytes, which displayed a hyperpolarization-induced inward current that was enhanced by cGMP as well as cAMP. Similarly to its homologs in other animals, acHCN is permeable to K + and Na + ions, and is selectively blocked by Cs + and ZD7288. We found that acHCN is predominantly expressed in inter-and motor neurons, including LFS siphon motor neurons, and therefore tested whether HCN channels are involved in simple forms of learning of the siphon-withdrawal reflex in a semiintact preparation. ZD7288 (100 μM) significantly reduced an associative form of learning (classical conditioning) but had no effect on two nonassociative forms of learning (intermediate-term sensitization and unpaired training) or baseline responses. The HCN current is enhanced by nitric oxide (NO), which may explain the postsynaptic role of NO during conditioning. HCN current in turn enhances the NMDA-like current in the motor neurons, suggesting that HCN channels contribute to conditioning through this pathway.HCN channels | learning and memory | NMDA | nitric oxide | Aplysia H yperpolarization-activated, cyclic nucleotide-gated (HCN), cation nonselective ion channels generate hyperpolarization-activated inward currents (I h ) and thus tend to stabilize membrane potential (1-3). In addition, binding of cyclic nucleotides (cAMP and cGMP) to the C-terminal cyclic nucleotide binding domain (CNBD) enhances I h and thus couples membrane excitability with intracellular signaling pathways (2, 4). HCN channels are widely important for numerous systemic functions such as hormonal regulation, heart contractility, epilepsy, pain, central pattern generation, sensory perception (4-15), and learning and memory (16-24).However, in previous studies it has been difficult to relate the cellular effects of HCN channels directly to their behavioral effects, because of the immense complexity of the mammalian brain. We have therefore investigated the role of HCN channels in Aplysia, which has a numerically simpler nervous system (25). We first identified and characterized an HCN gene in Aplysia, and showed that it codes for a channel that has many similarities to the mammalian HCN channel. We found that the Aplysia HCN channel is predominantly expressed in motor neurons including LFS neurons in the siphon withdrawal reflex circuit (26, 27). We therefore investigated simple forms of learning of that reflex in a semiintact preparation (28-30) and found that HCN current is involved in classical conditioning and enhances the ...